Railway traffic controlling apparatus



Aug. 13, i946. H. A. THOMPSONA RAILWAY ATRAFFIC CONTROLLING APPARATUS 2 Sheets-Sheet' l Filed Feb. 19, 1944' ,N .@mwml NA. 1 C

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n. mmf. m. o .@RQQMK 1 Qwmnwm m QH @Sb um# @www @Y Patented Aug. 13, 1946 RAILWAY TRAFFIC CONTROLLING APPARATUS Howard A. Thompson, Edgewood, Pa., assigner to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application February 19, 1944, Serial No. .523,065

7 Claims.

My invention relates to railway traflc controlling apparatus, and particularly to apparatus employing track circuits supplied with periodically interrupted or coded current for controlling Wayside and/ or cab signals.

The principal object of my invention is to improve the shunting sensitivity of track circuits of the type described.

Another object of my invention is the provision of means for supplying to a coded track circuit a high voltage impulseouring the on period of each code cycle in a way which does not increase Wear on the contacts of the coding relays.

A further object of my invention is to provide novel means for checking that a high voltage impulse is actually present during the on period of each code cycle.

According to my invention, I connect the secondaiy winding of an impulse transformer in seriesA with the track battery from which coded current is normally supplied to the track circuit, and I energize the secondary winding of this transformer over a contact of the relay which codes the track circuit energy in a manner to cause the transformer to supply to the track circuit during the on period of each code cycle a high voltage impulse of less duration than the on period of the code cycle, whereby the coding relay contacts do not interrupt the high voltage energy. I further connect in series with the track battery and the secondary winding of the impulse transformer the one winding of a two winding high voltage checking relay and a front contact of a rst repeater of this checking relay. The other winding of the high voltage relay is constantly connected to a source of direct current, and the parts are so proportioned that when said one winding is deenergized the relay will close a normal contact, but that, each time a high voltage impulse is supplied to the track circuit the resultant energization of said one winding by this impulse will cause the relay to close a reverse contact. A second repeater of the checking relay is energized over said reverse contact in` such manner that this relay will remain continuously energized as long as said high voltage relay operates its contacts in step with the code, and said rst repeater relay is energized over said normal contact and a front contact of said seco-nd repeater relay in such manner that it will remain continuously energized as long as said second relay is energized and said high voltage relay continues to operate its contacts in step with the code.

In an alternative arrangement, I employ in place of the high voltage relay at the battery end of the track circuit and the two repeaters of this relay for checking that a high voltage impulse is being supplied to the track circuit during each on period of the code in the intended manner, another high voltage relay having its one winding connected in multiple with the track relay and its other winding connected to a suitable source of current over a stick circuit including its own front contact and a contact of the track relayl This latter relay performs the same functions that are performed by the track relay in the arrangement rst described.

Other objects and characteristic features of my invention will become apparent as the description proceeds.

I shall describe two forms of signaling systems embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic View showing one form of apparatus embodying my invention. Fig. 2 is a diagrammatic view showing the nature of the track circuit current obtained with the apparatus shown in Fig. 1. Fig, 3 is a View similar to Fig. 1 showing a modification of the apparatus illustrated in Fig. l, and also embodying my invention. Fig. 4 is a diagrammatic view showing the nature of the track circuit current with the apparatus shown in Fig. 3.

Similar reference characters refer t0 similar parts in each of the several views.

Referring first to Fig. 1, the reference characters l and la designate the track rails of a stretch of railway track over which traiic normally moves in the direction indicated by the arrow, that is to say, from left to right in the drawings. These rails are divided by means of insulated joints 2 into blocks, only one of which E--G is shown complete in the drawings, and this block, in turn, is further divided at point F by means of other insulated joints 2 to form two track sections IT and AIT.

Traiic entering each block is controlled by a signal designated by the reference character S with a distinguishingsufx corresponding to the location. These signals may be of any suitable type, but in the well known form here shown these signals are color light signals and each comprises a red lamp R, a yellow lamp Y, and a green lamp G, which lamps when illuminated indicate stop, approach and clean respectively.

Eachtrack section is provided with a track circuit comprising a code following track relay connected across the rails at the entering end of the section, andmeans located at the leaving end of the section for supplying to the rails of the section coded direct current the code frequency of which is controlled by traiiic conditions in advance. 5

Each code following track relay is designated by the reference character R with a prefix corresponding to the reference character for the associated section, and may be of any suitable type capable of operating its contacts in step Al0 with the pulses of coded current supplied to .the rails. In actual practice each of these relays will usually be of the biased polar type because of the greater sensitivity of this type of relay.

The means located at the leaving end .of each section for supplying coded current to the rails of the associated section varies slightly accord-- ing as these means are disposed at a signal location or at a cut section location. Referring par ticularly to the means located at the signal loca- L tion YG, which means are typical of the means located at each of the other signal locations, these means in the form here illustrated `cornprise a battery o connected across the rails in series with the front contact 5 of a code repeater 3:. relay iCTM, a current limiting resistance 6, the secondary winding I of a transformer TG, the one -winding 8 of a two winding high voltage polar stick checking relay II-WR, and the front contact S-Qa of a iirst repeater relay II-IVBSA 3o of the associated checking relay.

The code repeater relay ICTM may be controlled through the medium of the track Vrelay for the section next in advance ina well known manner not shown to cause it to operate its contacts 5 and Il at one or another of therusual plurality of code rates. Selection .among these code rates, which rates in actual practice in a three block signaling system will usually comprise 75 or 18() times per minute depending upon 'whether the block to the right of block E-G is occupied or unoccupied, may be made Vby Ythe usual decoding ,apparatus It controlled by the track relay AZTR for the track section AZT, It will be seen, therefore, that when relay ICTM. is operating, the resultant .operation `of its contact 5 will act to :interrupt or `code the current supplied by the associated track battery li Aat "75 or 180 times per minute ldepending upon whether the block to the right of section E-G lis occu. `r pied or unoccupied. Each interruption is of such duration that the resulting code will consist of code cycles each comprising substantially equal on and off periods.

The contact II of relay ICTM controls 'the -supc55 ply of current to an energizing circuit for the primary winding I2 of transformer TG. This energizing circuit includes in addition to the contact EI, a suitable source of current the positive and negative terminals of which are designated B and C, respectively, and a condenser I3 con'- nected in multiple with the primary winding I2.

It will be seen, therefore, that each time vrelay ICTM closes its back contact it, energy will be stored in the magnetic circuit of transformer TG o5 and also iin condenser I3, whereas each ltime relay ICTM opens contact II, the energy stored in the transformer and condenser will cause a relatively high electromotive force to be induced inthe secondary winding 'I of transformer TG. The contacts 5 and `II of relay :ICTM are so adjusted that this induced electromotive force will be initiated immediately after the closing of contact .5, and will'be substantially expended before contact'E again opens, and it follows that 5f i with the parts arranged in this manner a high Voltage impulse will be impressed on the rails of the associated section during each "on period of the code, but that this electromotive force will not increase the wear on the contacts of relay ICTM since these contacts do not interrupt the circuit during the presence of this impulse. It will be obvious, of course, that a voltage will also be induced in secondary winding l of transformer TG each time the energizing circuit for primary winding I2 becomes closed at contact I1I, but due to the previously referred to adjustment of the contacts 5 and II, and the time constants of the circuit, the magnitude of this electromotive lforce will be negligible insofar as the Voperation of the contact 5 is concerned, and no Vappreciable Voltage will be impressed on the rails due to the closing of the contact I i. The nature of the .resulting code is illustrated diagrammatically in Fig. 2, where curve b represents the approach or 75 code and curve c represents the clear or 180 code.

The winding I5 of the high voltage relay iHVR is constantly energized by an associated battery I6, and the parts of this relay are so proportioned that when the winding I5 only is energized, as will be the case during the off periods of the code, the contact I'i-la will become closed. However, when the winding 8 is also energized, as will be the case during the on periods of .the code, a flux is set up in the core of the relay by the current flowing in the winding 8 which flux opposes that due to the current flowing in winding I5, and the parts are further so proportioned that under these conditions the relay will close its contact I'l-I'Ib if the high Voltage impulse is present but will retain its contact I'I--I Ia Vclosed if the high voltage impulse is absent. It follows, therefore, that the relay IHVR will alternately open and close its contacts Il-I'Ia and l'I-I'Ib in step with the coded current supplied to the rails I and Vict if the high voltage impulse is present during each on period of the code, but will retain its contacts I-ila continuously closed if this high voltage impulse is absent.

The repeater relay Il-IVBSA referred to hereinbefore is energized over a circuit which Vpasses from terminal B of the source through contact II-I'Ia of relay IHVR, a front contact I8 of a second repeater relay {HVFSA and a resistance `I5 connected in multiple with the winding of relay II-IVBSA to terminal C. The second repeater relay IHVFSA, in turn, is energized over a circuit which passes from terminal B through contact II'Ilb of relay IHVR, and a condenser 20 connected in multiple with the winding of relay IHVFSA to terminal C. It will be seen, therefore, that when relay IHVR is operating, relay IHVFSA will become energized each time contact I'l-IIb of relay Ill-IVR becomes closed. The condenser 20 renders the relay IHVFSA slow to release, and the parts are so proportioned that relay IHVFSA will maintain its front contact I8 continuously closed as long as relay IHVR continues to alternately open and close its contacts at any one of the usual code rates.

As long as contact I8 of relay lHVFSA remains closed, relay IHVBSA will become ener- 'gized each time relay IHVR closes its contact II-IIa, and the relay II-IVBSA is rendered sufciently slow releasing by the resistance I9 so that it will maintain its front contact continuously closed as long as relay IHVR continues to follow the code.

It Will benoted that the snub or closed circuit ate at the 75 code rate, and signal SE willthereupon display its approach aspect.

The parts Will remain in the positions just described until the train vacates the block of which section AZT forms a part. When this happens, the 75 code energy will be supplied to section A2T and track relay AZTR will follow this code and will act through the decoding apparatus i to cause signal SG to display its approach aspect. Furthermore, relay l CTM will start to operate at the rate of 180 times a minute, and Will thus cause 180 code to be supplied to section IT, and hence to section Ai T, whereupon signal SE will display its proceed aspect.

When the train vacates the block next in advance of the block of which section AZT forms part, signal SG will display its proceed aspect and all parts will be restored to the positions in which they are shown in the drawings.

It should be particularly pointed out that with the apparatus constructed in the manner described, the presence of the high voltage impulse during the on period of each code cycle acts to break down any high resistance lm or coating which may be present on the rails, thereby insuring a shunting effect of the Wheels and axles of a car or train under conditions where a'lower voltage Would be insufcient. The magnitude of the high voltage impulses may be made many times the usual track circuit voltage, and since no part of the high voltage impulse is present at the time the coding contacts of the various coding relays are either opening or closing,vtl1e pres ence of these impulses does not produce additional wear on these contacts. It might also be mentioned that since a high voltage impulse is present during each on period of the code, these impulses are available to break down the resistance of the wheel to rail contacts as the car or train moves from point to point along the track.

It should also be particularly pointed out that with the apparatus constructed in the manner just described if the high voltage impulse fails for any reason, the resultant underenergization of the winding 8 of the associated high voltage relay will result in the failure of this relay to operate its contacts in step with the code, and will thus cause the associated BSA checking relay to become deenergized. The deenergization of this relay will interrupt the track circuit at its front contact S-Sa, and Will thus cut off the supply of coded energy to the track relay. This will result in the signals moving to their Stop positions so that the failure Will be sure to be quickly detected.

Referring now to Fig. 3, I have here shown an alternative arrangement of circuits in which an auxiliary code following repeater relay ICTMM of relay ICTM is provided at location G for controlling the energization of the primary Winding i2 of transformer TG, and a similar repeater relay ITM controlled by an auxiliary track relay ETR/A presently to be described is provided at location F for controlling the energization of the secondary winding l2 of transformer TF. The energizing circuits for relays ICTMM and ITM are obvious from an inspection of the drawings, and it Iwill be apparent that each time relay lCTM or auxiliary track relay ITRA becomes energized, the associated repeater relay will become energized at the expiration of a short time interval thereafter. The primary winding i2 of transformer TG is energized over back contact 22 of relay ICTMM, while that of transformer TF is energized over front contact 22 of relay ITM because of the fact that back contact coding is em'- ployed at location F, as pointed out hereinbefore. With this arrangement, the energizing circuits for the primary windings of the transformers TG and TF Will not become interrupted until the expiration of a short time interval after the on period of the code is established by the closing of the front contact 5 of relay ICTM or the back contact 5 of relay ITRA, and it follows therefore that the high voltage impulse Will not be established until a short period after the start of the on period of each code cycle. This is shown diagrammatically in Fig. 4. This arrangement provides more positive action and consequently more positive protection against burning of the contacts than is provided with the apparatus shown in Fig. l as a consequence of the fact that the high voltage impulse is initiated substantially simultaneously with the establishment of the on period of the code.

Furthermore, in the alternative arrangement of circuits shown in Fig. 3, I employ in place of the high voltage checking relay and the associated front and back contact repeaters of these relays a't the battery end of each track circuit to check that a high voltage impulse is being supplied to the associated track circuit during each on period of th'e code in the intended manner, an auxiliary track relay located at the track relay end of the track circuit. These auxiliary track relays are designated by the same reference characters as the reference characters for the associated track relay with the sufnxA, and may be generally similar to the track relays except for the fact 'that each relay is provided with two windings. The winding 8 of each of these auxiliary relays'v is connected in multiple with the Winding of the associated track relay, while the other Winding l 5 of each of these auxiliary relays is energized over a stick circuit which includes a battery 2t, a front contact 2s of the associated track relay and its own front contact 25. The parts of each of these auxiliary relays are so proportioned that th'e relay Will become energized to a sucient extent to cause it to close its front contacts during each on period of the code if and only if the high voltage impulse is present, and that when either one of these relays closes its front contact 25, the energy supplied to its winding l5 over the associated stick circuit will then be sufficient to retain the front contacts closed during the remainder of th'e on period which caused the contacts to become closed. If the stick circuits were not provided, the auxiliary relays would be only momentarily energized during the high Voltage impulse, and the stick circuits provide a means for insuring that .the front and back contacts of the auxiliary track relays will be closed for approximately equal periods of time.

The auxiliary track relays may be utilized to perform the functions that are performed by the regular track relays in Fig. 1, and When so used, if the high voltage impulse is not present during the on periods of the code, the auxiliary relays will fail to operate. This will cause the signals to indicate stop and will thus result in immediate detection of the failure.

The operation as a whole sh'own in Fig. 3 is generally similar to the operation of the apparatus shown in Fig. 1, and it is accordinglybelieved that this operation will be apparent from the foregoing description and from an inspectionof the drawings Without further de'- tailed description.

of the apparatus `scarico which is provided for relay ,II-IVFSA to Vrender it slow releasing comprises a condenser, While that provided Vfor .relay IHVBSA comprises Ia resister. The reason .for this diiierence Ain the snubs for the -tWo relays is that the contact I'l-I'Ia of relay -IHVR -is closed for .a shorter portion of each code vcycle than the contact Il-Ilb, Aand a resistor snub will not provide a 'suiiciently slow release time for the relay II-lV-FSA.

rIt will also be noted `that while relays II-IVFSA and 'II-IVBSA will both he energized as long as relay IHVR, follows the code, if relay II-IVR stops following the code for any reason jrelay II-IVBSA Awill become deenergized and will open its front contact S-Sa and close its back .contact 9-911 The opening of contact S-Sa will disconnect the `battery 4 and :secondary winding l of transformer TG from the track circuit-while the closing of back contact V9--Sli will complete a restoring circuit for relay II-IVR. passing vfrom battery 4 through resistor 5, secondary winding 'I `of transformer TG, winding 8 of relay IHVR, back contact S-Sb of relay lli-IVBSA and contact of relay I CTM to battery 4. This latter circuit permits the equipment to reset itself should the coding action oi relay ICTM be stopped for any reason.

Referring now to the cut section location F, the means here shown for supplying coded current to the rails of section AIT is identical with that just described at location `Gf for supplying coded current kto the rails of section IT except for the fact that the coding action at this location instead of being effected by means of a code re- .peater lrelay is effected by the track relay ITR. which "functions to repeat the code to section AIT. Itis believed -to be unnecessary therefore to describe this means in detail. It should be noted,

however, that the contact 5 of relay lTR which s.

eiects the coding of the track circuit energy is a back contact, while the contact I I of relay ITR which controls the -energization of the primary winding I2 of transformer TF is a front contact so that the on periods of the code in section AIT occur during the Voli period of the code in section IT. The use of a back contact of the track relay at the cut section location instead of a front contact to repeat the code is a wellknown expedient to minimize code distortion,

and for the purpose of my present invention it is immaterial Whether a back or a front contact is employed.

The track relays AITR and A2'IR control the associated signals YSE .and SG through the medium of suitable decoding apparatus IEB. This decoding apparatus may, for example, be similar lto that shown and described in Letters Patent of the United States No. 2,218,l20, granted to Frank H. Nicholson and Leslie R. Allison on October 15, 1940, -for Railway traiiic controlling apparatus, land it is believed, therefore, that for `purposes of the present application it is sufficient to point out that the lamp G, Y, or R of these signals will -be lit to indicate clean approach, or stop .according as the associated track relay is supplied with 180 code, 75 code, or no code.

As shown in the drawings, sections AIT, IT and `AZT are all unoccupied, and assuming that the section next in Vadvance of section AZT is also unoccupied, all three of the sections AIT, IT and AZT will be supplied with 180 code energy. Signals SG and SE will therefore both indicate proceed.

In explaining the operation cf the apparatus 6 as a whole, I shall assume that a train lmoves from left to right over vthe stretch of track shown in the drawings.` When the train enters section AIT, the train shunt will cut ol the supply of coded energy to the track relay AITR, and this track relay will therefore become deenergized and will cause signal SE to display its stop aspect.

When the train enters section IT, track relay ITR. will become deenergized. This will cut off the supply of coded current to section A'iT and also to winding 8 of relay AIHVR, and contact H-Ha of relay AI-HVR will `therefore become closed, so that relay AIHVFSA will now become deenergized and will deenergize relay AIHVBSA. The deenergization of relay AIHVBSA will complete t-he restoring circuit for winding 8 of relay AIHVR, .but since this circuit -will not be supplied With high voltage impulses under these conditions, contact -I Y'l--I'la of relay AIHVR will remain continuously closed. Furthermore, due to the absence of coded current in section AIT track relay AITR, will now remain deenergized, and will cause signal SE to continue to display its stop aspect even though the train completely vacates section AIT.

When the train enters section AZT, track relay AZTR. will become deenergized and will cause signal SG to display its stop aspect. The deenergization of track relay AQTR will falso function through the medium of the decoding apparatus Ill to cause relay ICTM to operate at the rate of times per minute, but this change in the rate of operation of relay ICTM will not have any eect on the remainder of the apparatus as long as any part oi the train remains in section IT.

However, as soon as the train vacates section iT, the resultant removal of the `train shunt permits the F5 code energy supplied to the rails of section IT to operate track relay ITR. The first time relay ITR picks up and Acloses its front contact I I, energy becomes stored in the transformer TF, and when this relay next releases and closes its back contact 5, lthis stored energy causes a high voltage impulse to be supplied to the winding 3 `of relay AIX-IVR by virtue of the restoring circuit which i's then closed at back Contact 5 of relay ITR and at back contact Q-b of relay AIHVBSA. This high voltage impulse causes relay AIHVR to open its contact 'I1-Ila and close its contact I'I-Ib, whereupon relay AIHVFSA picks up. Due to the previously described proportioning of the parts, the duration of this high voltage impulse is relatively short, and on the termination of this impulse the energy supplied to Winding I5 of relay All-IVR from battery I causes contact I'l-Ib to open and contact H-Ila to again close. Since contact I3 of relay AiI-IVESA is closed when contact I-I'lc hecornes closed under these conditions, the closing of 'Contact Il--I'Ic completes the energizing circuit iOr relay AEHVBSA and this relay then picks up. The picking up of this relay, in turn, interrupts the restoring circuit for relay AIHVR and reestablishes the track circuit, so that subsequent operation of the track relay lTR in step with the coded current supplied to track section IT causes coded current of the same frequency to he supplied to .section AET.. The proportioning of the parts is preferably such that the interruption of the restoring circuit for relay AIHVR due to the picking up of .relay AII-WBSA will not occur during the duration of the high voltage impulse so that the contact S-Eb does not have to be a high voltage contact. The .coded current supplied to section AIT will cause track relay AITR to oper- Although I have herein shown and described only two forms of signaling systems embodying my invention, it is understood that various changes and modications may be made th'erein within the scope of the appended claims without, departing from the spirit and scope of my inven. tion; Y*

Having thus described my invention, what I claim is: v

1. In combination, a section of railway track, means for supplying coded signaling energy consisting of alternate on and oli periods tothe rails of said section, a track relay connected' across the rails of said section and responsive toA said coded energy, means for supplying to the rails of said section during each on period of the code a high voltage impulse of less duration th'an the on period to increase the shunting sensitivity of the track circuit formed by said track relay and the rails of said section, and means for detecting the presence of said high voltage impulse comprising e, relay subjected to the track circuit energy and operable from one position to another if and only if said high voltage impulse is present during each on period.

2. In combinatio-n, a section of railway track, a coding relay having a iirst Contact which is a1- ternately opened and closed when said relay is operating and a second contact which' becomes opened each time said first contact becomes closed, a source of track circuit current, an impulse transformer having its secondary winding connected across the rails of said section in series with said source and said rst Contact of said coding relay, a circuit for the primary winding of said impulse transformer including a source of current and said second Contact, and a track relay connected across the rails of said section and responsive to the current supplied to the rails from said source of track circuit current over said iirst contact.

3. In combination, a section of railway track, means for supplying to the rails of said section coded signaling energy consisting of alternate Non!) DE having a high voltage impulse superimposed thereon, a checking relay subjected to said coded energy and operable in step with the code if and only if said high voltage impulse is present, and means controlled by said checking relay for interrupting the supply of coded energy to the rails of said section if said high voltage impulse is absent from the code.

4. In combination, a section of railway track, a coding relay having a first contact which is alternately opened and closed when said relay is operating and a second contact which becomes opened each time said rst contact becomes closed, an impulse transformer having a primary and a secondary winding, a two winding polar' stick checkingrelay; means comprising a source periods, each said on period source of current and said first polar contact,

an energizingv circuit for said first repeater-relay including a source 'of current, said second polar contact and a front contact 'of said second repeater relay, and means for rendering said repeater relays sufficiently slow acting to maintain their armatures in their attracted positions of track circuit current connected across the rails f of said section in series with said rst contact of said coding rela the secondary winding of said impulse transformer, the one winding of said two winding checking relay, and a front contact of a rst repeater relay for supplying coded signaling energy consisting of alternate on and oli periods to the rails of said section, a track relay connected across the rails of said section and responsive to said coded signaling energy, means including a source of current and said second contact of said coding relay for energizing said primary winding to thereby induce in said secondary winding a high voltage whenever said checking relay is operating in response to the coded energy flowing in its said one winding.

5. In combination, a section of railway track, a coding relay having a rst contact which is alternately opened and closed when said relay is operating and a second contact which becomes opened each time said first contact becomes closed, an impulse transformer having a primary and a secondary winding, a two winding polar stick checking relay; means comprising a source of track circuit current connected across the rails of said section in series with said first contact of said coding relay, the secondary winding of said impulse transformer, the one winding of said two Winding checking relay, and a front contact of a rst repeater relay for supplying coded signaling energy consisting of alternate on and oir periods to the rails of said section, a track relay connected across the rails of said section and responsive to said coded signaling energy, means including a source of current and said second contact of said coding relay for energizing said primary winding to thereby induce in said secondary winding a high voltage impulse during each on period of the code, means for constantly energizing the other winding of said checking relay, the parts being so proportioned that said checking relay will close a lirst polar contact during each on period of the code if and only if said high volta-ge impulse is present and a second polar contact at all other times, a second repeater relay, anenergizing circuit'for said second repeater relay including a source of current and said irst polar contact, an energizing circuit for said first repeater relay including a source of current, said second polar contact and a front contact of said second repeater relay, means for rendering said repeater relays sufciently slow acting to maintain their armatures in their attracted positions whenever said checking relay is operating in response to the coded energy flowing in its said one winding, and a restoring circuit for said checking relay including'said rst Contact of said coding relay, said source of track circuit current, the secondary winding of said impulse transformer, and a back contact of said rst repeater relay.

6. In combination, a section of railway track, a rst relay having a pair of contacts which are alternately opened and closed when said relay is operating, an impulse transformer having a primary and a secondary winding, a source vof track circuit current connected across the rails of said section in series with one of the contacts of said first relay and the secondary winding of said transformer for supplying to the rails of said section coded signaling energy consisting of alternate on and oil periods, a track relay connected across `the rails of said section and responsive to said 'coded current, a repeater relay provided with a contact and energized over the other contact of said rst relay in such manner that said repeater relay will open its contact at the expiration of a short interval of time after said one Contact of said first relay becomes closed, and means controlled by the contact of said repeater relay for energizing said primary Winding of saidV transformer to thereby'induce in said secondarywinding during each on period of the code a high voltage impulse which increases the shunting sensitivity rof the track circuit formed by the rails of said section and said track relay.

7. In combination, a section of railway track,

means for supplying coded signaling energy con: sisting of alternate on and off" periods to the rails of said section, a trackV relay connected across the rails of said section and responsive to said coded energy, a two Winding auxiliary relay having one winding connected across the rails of said section and the other Winding connected with a source of current over its own front contact and a front contact of said track relay, vthe parts being so proportioned that said auxiliary relay will operate itsA contacts in step with the code if and only if said high voltage impulse is present during each on period of the code, and signaling means controlled by said auxiliary relay. s HOWARD A. THOMPSON. 

